Apparatus for making underground reservoir

ABSTRACT

A device for constructing an underground reservoir by dissolving limestone using carbon dioxide. The device includes a CO 2  storage tank; an absorption tower; a decompression valve; a gas-liquid separator; a crystallizer; a vacuum pump; a buffer tank; a first booster pump; a second booster pump; and a third booster pump. The decompression valve is connected to a limestone layer, and is connected to the gas-liquid separator. The absorption tower is connected between the gas-liquid separator and the limestone layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/351,138, filed Apr. 10, 2014, now pending, which is a National StageAppl. filed under 35 USC 371 of International Patent Application No.PCT/CN2012/074710 with an international filing date of Apr. 26, 2012,designating the United States, and further claims priority benefits toChinese Patent Application No. 201110117074.X filed May 6, 2011.Inquiries from the public to applicants or assignees concerning thisdocument or the related applications should be directed to: MatthiasScholl P. C., Attn.: Dr. Matthias Scholl Esq., 245 First Street, 18thFloor, and Cambridge, Mass. 02142.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to the construction of an underground reservoir ora cave depot, and more particularly to a method and device forconstruction of an underground reservoir or a cave depot in limestonegeology.

Description of the Related Art

Underground energy/waste reservoir can be used for storage of naturalgas, oil, and other energy resources, thereby being an indispensablepart for a large gas transmission trunk line system. Nuclear waste orcarbon dioxide can also be preserved in the underground energy/wastereservoir, which is conducive to national security, energy supply, andenvironmental improvement. Conventionally, large-scale undergroundenergy/waste reservoirs are generally constructed in mined oil and gasreservoirs, abandoned mines, underground saline aquifers and undergroundrock salt deposits. Limited by specific geological conditions, the oiland gas pipeline networks and the oil and gas consumption centers arenot necessarily located in a geological environment suitable forconstructing reservoirs, thereby greatly affecting the development ofthe underground repository. Thus, it is urgent to develop a universalmethod for construction of underground reservoirs in various geologicalzones. Limestone has a wide distribution in the stratum layer, lowpermeability, and good sealing performance. In the process ofdiagenesis, limestone is hardly affected by karstification, and thus thenatural fissures thereof do not expand, and are even filled with calciteand clay. Therefore, the underground limestone layer has the basicgeological conditions for constructing underground energy and wastereservoirs.

U.S. Pat. No. 7,156,579B2 discloses a method for constructing a gasreservoir in limestone layers. The method employs hydrochloric acid todissolve limestone to construct the gas reservoir. The chemical equationfor dissolving limestone is as follows:CaCO₃+2HCl→CaCl₂+CO₂+H₂O

As shown from the chemical equation, a large amount of carbon dioxide isproduced in the process of cavern making, which is apt to causegreenhouse effect and environmental pollution if not being dealtproperly.

SUMMARY OF THE INVENTION

In view of the above-described problems, it is one objective of theinvention to provide a method and a device for construction of anunderground reservoir or a cave depot in limestone geology. The methodand device, on one hand, solve the problem of greenhouse effectresulting from carbon dioxide emission, and on the other hand, provide anew way for utilizing carbon dioxide.

The main chemical composition of limestone is calcium carbonate (CaCO₃),which is soluble in a solution comprising carbon dioxide to yieldcalcium bicarbonate solution. The chemical equation is as follows:CO₂+H₂O+CaCO₃⇄ Ca(HCO₃)₂

The dissolution process is a reversible reaction. The change oftemperature and partial pressure of CO₂ can significantly affect thedissolution equilibrium. Lowering the reaction temperature andincreasing the partial pressure of CO₂ can drive the equilibrium toshift to the right, thereby promoting the dissolution of CaCO₃.Conversely, enhancing the reaction temperature and decreasing thepartial pressure of CO₂ can promote calcium bicarbonate to decompose andyield calcium carbonate, water, and carbon dioxide. Based on the theory,high pressure of carbon dioxide solution is introduced into thelimestone layer to dissolve the limestone to yield calcium bicarbonatesolution. Thereafter, calcium bicarbonate precipitates by decompressionand is decomposed to yield calcium carbonate, water, and carbon dioxide.The gas, liquid, and solid are separated from each other. The collectedsolution can be used for dissolving carbon dioxide again. The collectedcarbon dioxide can be used for forming new carbon dioxide solution.

To achieve the above objective, in accordance with one embodiment of theinvention, there is provided a method for construction of an undergroundreservoir by dissolving limestone using carbon dioxide, the methodcomprising the steps of:

-   -   a) drilling a first well and a second well extending from a        ground to a limestone layer, disposing at least one channel in        the limestone layer to connect the first well and the second        well, and inserting a first sleeve and a second sleeve in the        first well and the second well, respectively;    -   b) introducing carbon dioxide having a gas pressure of at least        1 MPa into a carbon dioxide absorption solution having a        pressure of at least 1 MPa to yield a carbon dioxide solution,        injecting the carbon dioxide solution into the first sleeve and        allowing the carbon dioxide solution to flow to the limestone        layer through the first sleeve and react with limestone to yield        a calcium bicarbonate containing solution whereby forming a        cavern comprising solutions, and discharging the calcium        bicarbonate containing solution out of the second sleeve;    -   c) collecting and decompressing the discharged calcium        bicarbonate containing solution so that calcium bicarbonate        therein is decomposed to yield carbon dioxide, water, and        calcium carbonate, performing a gas, liquid, and solid        separation, collecting the separated carbon dioxide absorption        solution for a new round of dissolution of carbon dioxide,        collecting the separated carbon dioxide for a new round of        formation of the carbon dioxide solution, and storing the        separated calcium carbonate; and    -   d) repeating steps b) and c) until a desired cavern comprising        solutions is produced, discharging the solutions in the cavern        to yield the underground reservoir.

In a class of this embodiment, the gas pressure of the carbon dioxideintroduced into the carbon dioxide absorption solution is between 1 and15 MPa, and the pressure of the carbon dioxide absorption solution isbetween 1 and 15 MPa. Preferably, the gas pressure of the carbon dioxideintroduced into the carbon dioxide absorption solution is between 2 and6 MPa, and the pressure of the carbon dioxide absorption solution isbetween 2 and 6 MPa.

In a class of this embodiment, the carbon dioxide absorption solution isselected from the group consisting of water, between 0.001 and 10 mol/Lof sodium chloride solution, between 0.001 and 5 mol/L of sodium oxalatesolution, between 0.001 and 5 mol/L of sodium acetate solution, or amixture thereof.

In a class of this embodiment, the discharged calcium bicarbonatecontaining solution is decompressed at a temperature of between 20 and80° C. to have a pressure of between 5×10⁵ Pa and 1×10² Pa so thatcalcium bicarbonate therein is decomposed to yield carbon dioxide,water, and calcium carbonate. Preferably, the discharged calciumbicarbonate containing solution is decompressed at a temperature ofbetween 20 and 80° C. to have a pressure of between 1.01×10⁵ Pa and1×10³ Pa so that calcium bicarbonate therein is decomposed to yieldcarbon dioxide, water, and calcium carbonate.

The invention further provides a device for construction of anunderground reservoir by dissolving limestone using carbon dioxide, thedevice comprising: a CO₂ storage tank; an absorption tower; adecompression valve; a gas-liquid separator; a crystallizer; a vacuumpump; a buffer tank; a first booster pump; a second booster pump; and athird booster pump.

The absorption tower comprises a CO₂ gas inlet, a CO₂ gas outlet, a CO₂absorption solution inlet, and a CO₂ solution outlet. The CO₂ gas inletof the absorption tower is connected to a gas outlet of the CO₂ storagetank via a first pipe. The CO₂ absorption solution inlet of theabsorption tower is connected to a liquid outlet of the first boosterpump via a second pipe. The CO₂ gas outlet of the absorption tower isconnected to a gas inlet of the third booster pump via a third pipe. Agas inlet of the CO₂ storage tank is connected to gas outlets of thesecond booster pump and the third booster pump via pipes. The gas-liquidseparator comprises a CaHCO₃ solution inlet, a CO₂ gas outlet, and asolution outlet. The CaHCO₃ solution inlet is connected to a liquidoutlet of the decompression valve via a fourth pipe. The solution outletof the gas-liquid separator is connected to a solution inlet of thecrystallizer via a fifth pipe. The crystallizer comprises the solutioninlet, a CO₂ gas outlet, a CO₂ absorption solution outlet, and a CaCO₃slurry outlet. The CO₂ gas outlet is connected to an inlet of the vacuumpump via a sixth pipe. The CO₂ absorption solution outlet is connectedto a liquid inlet of the first booster pump via a seventh pipe. Theseventh pipe connecting the first booster pump and the crystallizer isprovided with a connector for supplementing the CO₂ absorption solution.A gas inlet of the buffer tank is connected to the CO₂ gas outlet of thegas-liquid separator and an outlet of the vacuum pump; and a gas outletof the buffer tank is connected to a gas inlet of the second boosterpump.

In a class of this embodiment, the crystallizer comprises a settlingchamber, a stripping chamber, a nozzle, a feeding pump, and a heatexchanger. The settling chamber comprises the CaCO₃ slurry outlet andthe CO₂ absorption solution outlet. The stripping chamber is disposedabove and communicates with the settling chamber. The CO₂ gas outlet isdisposed at the top of the stripping chamber. The nozzle is disposed inthe stripping chamber; a liquid inlet pipe of the nozzle is connected toa liquid outlet of the heat exchanger, and a liquid inlet of the heatexchanger is connected to a liquid outlet of the feeding pump, and aliquid inlet of the feeding pump is connected to the solution outlet ofthe gas-liquid separator.

Advantages of the invention are summarized below:

1. In contrast to the prior art, the method of the invention is moreenvironmentally friendly and provides a new way to utilized carbondioxide.

2. The byproduct of calcium carbonate produced by the invention is animportant industrial raw materials and industrial additives.

3. Through the method, natural gas, oil and other energy storagereservoirs can be constructed in oil and gas pipeline networks or theoil and gas consumption centers, which facilitates the energy supply.

4. The method and device of the invention are easy forindustrialization.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described hereinbelow with reference to accompanyingdrawings, in which:

FIG. 1 is an assembly diagram of a first well, a second well, a channelconnecting the first well and the second well, a first sleeve, and asecond sleeve according to a method for construction of an undergroundreservoir by dissolving limestone using carbon dioxide according to oneembodiment of the invention;

FIG. 2 is a schematic diagram of an underground reservoir constructedaccording to a method of the invention;

FIG. 3 is a schematic diagram of a device for construction of anunderground reservoir by dissolving limestone using carbon dioxideaccording to one embodiment of the invention; and

FIG. 4 is a schematic diagram of a crystallizer of a device forconstruction of an underground reservoir by dissolving limestone usingcarbon dioxide according to one embodiment of the invention.

In the drawings, the following reference numbers are used: 1. Ground; 2.Limestone layer; 3. First sleeve; 4.Second sleeve; 5. Channel; 6.Underground reservoir; 7. CO₂ storage tank; 8. Absorption tower; 9.Decompression valve; 10. Gas-liquid separator; 11. Crystallizer; 12.First booster pump; 13. Vacuum pump; 14. Buffer tank; 15. Second boosterpump; 16. Third booster pump; 17. Settling chamber; 18. Strippingchamber; 19. Nozzle; 20. CaCO₃ slurry outlet; 21. CO₂ absorptionsolution outlet; 22. CO₂ gas outlet; 23. Feeding pump; 24. Heatexchanger.

DETAILED DESCRIPTION OF THE EMBODIMENTS

For further illustrating the invention, experiments detailing a methodand device for construction of an underground reservoir by dissolvinglimestone using carbon dioxide are described below. It should be notedthat the following examples are intended to describe and not to limitthe invention.

Example 1

As shown in FIG. 3, a device for construction of an undergroundreservoir by dissolving limestone using carbon dioxide comprises a CO₂storage tank 7; an absorption tower 8; a decompression valve 9; agas-liquid separator 10; a crystallizer 11; a vacuum pump 13; a buffertank 14; a first booster pump 12; a second booster pump 15; and a thirdbooster pump 16, all of which employ conventional equipment manufacturedin accordance with the design specifications or purchased from chemicalmarkets. As shown in FIG. 4, the crystallizer 11 comprises a settlingchamber 17, a stripping chamber 18, a nozzle 19, a feeding pump 23, anda heat exchanger 24. The settling chamber 17 comprises a CaCO₃ slurryoutlet 20 at the bottom and a CO₂ absorption solution outlet 21 at thetop. The stripping chamber 18 is disposed above and communicates withthe settling chamber 17. The CO₂ gas outlet 22 is disposed at the top ofthe stripping chamber 18. The nozzle 19 is disposed in the strippingchamber 18. A liquid inlet pipe of the nozzle 19 is connected to aliquid outlet of the heat exchanger 24, and a liquid inlet of the heatexchanger 24 is connected to a liquid outlet of the feeding pump 23.

The CO₂ storage tank 7, the absorption tower 8, the decompression valve9, the gas-liquid separator 10, the crystallizer 11, the vacuum pump 13,the buffer tank 14, the first booster pump 12, the second booster pump15, and the third booster pump 16 are connected as follows.

The absorption tower 8 comprises a CO₂ gas inlet, a CO₂ gas outlet, aCO₂ absorption solution inlet, and a CO₂ solution outlet. The CO₂ gasinlet of the absorption tower 8 is connected to a gas outlet of the CO₂storage tank 7 via a first pipe. The CO₂ absorption solution inlet ofthe absorption tower 8 is connected to a liquid outlet of the firstbooster pump 12 via a second pipe. The CO₂ gas outlet of the absorptiontower 8 is connected to a gas inlet of the third booster pump 16 via athird pipe; a gas inlet of the CO₂ storage tank 7 is connected to gasoutlets of the second booster pump 15 and the third booster pump 16 viapipes. The gas-liquid separator 10 comprises a CaHCO₃ solution inlet, aCO₂ gas outlet, and a solution outlet. The CaHCO₃ solution inlet isconnected to a liquid outlet of the decompression valve 9 via a fourthpipe. The solution outlet of the gas-liquid separator 10 is connected toa solution inlet of the crystallizer 11 via a fifth pipe. Thecrystallizer 11 comprises the solution inlet, a CO₂ gas outlet, a CO₂absorption solution outlet, and a CaCO₃ slurry outlet. The CO₂ gasoutlet is connected to an inlet of the vacuum pump 13 via a sixth pipe.The CO₂ absorption solution outlet is connected to a liquid inlet of thefirst booster pump 12 via a seventh pipe. The seventh pipe connectingthe first booster pump 12 and the crystallizer 11 is provided with aconnector for supplementing the CO₂ absorption solution; and a gas inletof the buffer tank 14 is connected to the CO₂ gas outlet of thegas-liquid separator 10 and an outlet of the vacuum pump 13; and a gasoutlet of the buffer tank 14 is connected to a gas inlet of the secondbooster pump 15.

Example 2

A method for construction of an underground reservoir by dissolvinglimestone using carbon dioxide by the device in Example 1 is describedas follows.

a) A first well and a second well extending from a ground to a limestonelayer are drilled. At least one channel 5 is disposed in the limestonelayer to connect the first well and the second well. The first sleeve 3and the second sleeve 4 (as shown in FIG. 1) are disposed in the firstwell and the second well, respectively. The first sleeve 3 is connectedto the CO₂ solution outlet of the absorption tower 8 of the device inExample 1 , and the second sleeve 4 is connected to the liquid inlet ofthe decompression valve 9.

b) Carbon dioxide having a gas pressure of 3 MPa in the CO₂ storage tank7 is introduced to the absorption tower where carbon dioxide is absorbedby 2 mol/L of NaCl solution having a pressure of 3 MPa to yield a carbondioxide solution. Unabsorbed carbon dioxide is discharged from the CO₂gas outlet disposed at the top of the absorption tower 8, pressurized to3 MPa by the third booster pump 16 and finally returns to the CO₂storage tank 7. The carbon dioxide solution is injected into the firstsleeve 3 and flows to the limestone layer through the first sleeve 3 toreact with limestone to yield a calcium bicarbonate containing solution.Thus, a cavern comprising solutions is formed. The calcium bicarbonatecontaining solution is discharged out of the second sleeve 4.

c) The discharged calcium bicarbonate containing solution is collected,decompressed to normal pressure by the decompression valve 9, and thenis transported to the gas-liquid separator 10. Thereafter, the carbondioxide dissolved in the calcium bicarbonate containing solution isdischarged from the CO₂ gas outlet of the gas-liquid separator 10,transported to the buffer tank 14, and then to the second booster pump15 via pipes. In the second booster pump 15, the carbon dioxide ispressurized to have a gas pressure of 3 MPa and then transported to theCO₂ storage tank 7. The solution is discharged from the solution outletof the gas-liquid separator 10, and transported to the heat exchanger 24via the feeding pump 23 of the crystallizer. In the heat exchanger 24,the solution is heated to 40° C.±5° C. and transported to the nozzle 19disposed in the stripping chamber. The vacuum degree of the strippingchamber 18 and the settling chamber 17 of the crystallizer is controlledat a pressure of between 100 and 500 Pa. The temperature is controlledat 35° C.±5° C. Thereafter, the calcium bicarbonate containing solutionis decomposed to yield carbon dioxide, water, and calcium carbonate. Bythe pumping of the vacuum pump 13, carbon dioxide is discharged from theCO₂ gas outlet 22 disposed at the top of the stripping chamber 18,transported to the buffer tank 14 and the second booster pump 15 wherethe pressure of carbon dioxide is enhanced to 3 MPa, and finally returnsto the CO₂ storage tank 7. The liquid material enters the settlingchamber 17 of the crystallizer and calcium carbonate crystallizes,precipitates, and is discharged from the CaCO₃ slurry outlet 20. TheNaCl solution is discharged from the CO₂ absorption solution outlet 21disposed at the top of the settling chamber, mixed with a NaClreplenisher, pressurized by the first booster pump 12 to have a pressureof 3 MPa, and transported once again to the absorption tower 8.

Steps b) and c) are repeated until a desired cavern comprising solutionsis produced. Stop injecting the carbon dioxide solution to the firstsleeve 3. Compressed air is pumped into the first sleeve 3 so as toexpel the solutions in the cavern to yield the underground reservoir 6(as shown in FIG. 2).

Example 3

A method for construction of an underground reservoir by dissolvinglimestone using carbon dioxide by the device in Example 1 is describedas follows.

a) The step is the same as that in Example 2.

b) Carbon dioxide having a gas pressure of 5 MPa in the CO₂ storage tank7 is introduced to the absorption tower where carbon dioxide is absorbedby 0.05 mol/L of sodium acetate solution having a pressure of 5 MPa toyield a carbon dioxide solution. Unabsorbed carbon dioxide is dischargedfrom the CO₂ gas outlet disposed at the top of the absorption tower 8,pressurized to 5 MPa by the third booster pump 16 and finally returns tothe CO₂ storage tank 7. The carbon dioxide solution is injected into thefirst sleeve 3 and flows to the limestone layer through the first sleeve3 to react with limestone to yield a calcium bicarbonate containingsolution. Thus, a cavern comprising solutions is formed. The calciumbicarbonate containing solution is discharged out of the second sleeve4.

c) The discharged calcium bicarbonate containing solution is collected,decompressed to normal pressure by the decompression valve 9, and thenis transported to the gas-liquid separator 10. Thereafter, the carbondioxide dissolved in the calcium bicarbonate containing solution isdischarged from the CO₂ gas outlet of the gas-liquid separator 10,transported to the buffer tank 14, and then to the second booster pump15 via pipes. In the second booster pump 15, the carbon dioxide ispressurized to have a gas pressure of 5 MPa and then transported to theCO₂ storage tank 7. The solution is discharged from the solution outletof the gas-liquid separator 10, and transported to the heat exchanger 24via the feeding pump 23 of the crystallizer. In the heat exchanger 24,the solution is heated to 45° C.±5° C. and transported to the nozzle 19disposed in the stripping chamber. The stripping chamber 18 and thesettling chamber 17 work in the normal pressure (the vacuum pump in theexample is in nonuse). The temperature is controlled at 40° C.±5° C.Thereafter, the calcium bicarbonate containing solution is decomposed toyield carbon dioxide, water, and calcium carbonate. By the pumping ofthe vacuum pump 13, carbon dioxide is discharged from the CO₂ gas outlet22 disposed at the top of the stripping chamber 18, transported to thebuffer tank 14 and the second booster pump 15 where the pressure ofcarbon dioxide is enhanced to 5 MPa, and finally returns to the CO₂storage tank 7. The liquid material enters the settling chamber 17 ofthe crystallizer and calcium carbonate crystallizes, precipitates, andis discharged from the CaCO₃ slurry outlet 20. The NaCl solution isdischarged from the CO₂ absorption solution outlet 21 disposed at thetop of the settling chamber, mixed with a NaCl replenisher, pressurizedby the first booster pump 12 to have a pressure of 5 MPa, andtransported once again to the absorption tower 8.

Steps b) and c) are repeated until a desired cavern comprising solutionsis produced. Stop injecting the carbon dioxide solution to the firstsleeve 3. Compressed methane is pumped into the first sleeve 3 so as toexpel the solutions in the cavern to yield the underground reservoir 6(as shown in FIG. 2).

The invention is not limited to above examples. For example, the gaspressure of carbon dioxide to be introduced to the CO₂ absorptionsolution can be any pressure between 1 and 15 MPa, the pressure of theCO₂ absorption solution can be any pressure between 1 and 15 MPa. Thecarbon dioxide absorption solution is selected from the group consistingof sodium chloride solution, sodium oxalate solution, sodium acetatesolution, or a mixture thereof.

While particular embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention inits broader aspects, and therefore, the aim in the appended claims is tocover all such changes and modifications as fall within the true spiritand scope of the invention.

The invention claimed is:
 1. A device for constructing an undergroundreservoir by dissolving limestone using carbon dioxide, the devicecomprising: a) a CO₂ storage tank; b) an absorption tower; c) adecompression valve; d) a gas-liquid separator; e) a crystallizer; f) avacuum pump; g) a buffer tank; h) a first booster pump; i) a secondbooster pump; and j) a third booster pump; wherein the absorption towercomprises a CO₂ gas inlet, a CO₂ gas outlet, a CO₂ absorption solutioninlet, and a CO₂ solution outlet; the CO₂ gas inlet of the absorptiontower is connected to a gas outlet of the CO₂ storage tank via a firstpipe; the CO₂ absorption solution inlet of the absorption tower isconnected to a liquid outlet of the first booster pump via a secondpipe; the CO₂ gas outlet of the absorption tower is connected to a gasinlet of the third booster pump via a third pipe; a gas inlet of the CO₂storage tank is connected to a gas outlet of the second booster pump anda gas outlet of the third booster pump via pipes; the gas-liquidseparator comprises a CaHCO₃ solution inlet, a CO₂ gas outlet, and asolution outlet; the CaHCO₃ solution inlet is connected to a liquidoutlet of the decompression valve via a fourth pipe; the solution outletof the gas-liquid separator is connected to a solution inlet of thecrystallizer via a fifth pipe; the crystallizer comprises the solutioninlet, a CO₂ gas outlet, a CO₂ absorption solution outlet, and a CaCO₃slurry outlet; the CO₂ gas outlet is connected to an inlet of the vacuumpump via a sixth pipe; the CO₂ absorption solution outlet is connectedto a liquid inlet of the first booster pump via a seventh pipe; theseventh pipe connecting the first booster pump and the crystallizer isprovided with a connector for supplementing the CO₂ absorption solution;and a gas inlet of the buffer tank is connected to the CO₂ gas outlet ofthe gas-liquid separator and an outlet of the vacuum pump; and a gasoutlet of the buffer tank is connected to a gas inlet of the secondbooster pump.
 2. The device of claim 1, wherein the crystallizercomprises a settling chamber, a stripping chamber, a nozzle, a feedingpump, and a heat exchanger; the settling chamber comprises the CaCO₃slurry outlet and the CO₂ absorption solution outlet; the strippingchamber is disposed above and communicates with the settling chamber;the CO₂ gas outlet is disposed at the top of the stripping chamber; andthe nozzle is disposed in the stripping chamber; a liquid inlet pipe ofthe nozzle is connected to a liquid outlet of the heat exchanger, and aliquid inlet of the heat exchanger is connected to a liquid outlet ofthe feeding pump, and a liquid inlet of the feeding pump is connected tothe solution outlet of the gas-liquid separator.